The evolution of dark matter halo properties in clusters, filaments, sheets and voids     

Oliver Hahn  C. Marcella Carollo  Cristiano Porciani  Avishai Dekel 《Monthly notices of the Royal Astronomical Society》2007,381(1):41-51

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Pore water composition of volcanogenic sediments from across the Central American Subduction Zone     

Ulrike Schacht  Steffen Kutterolf  Oliver Bartdorff  Emelina Corrales Cordero 《Journal of Geochemical Exploration》2009

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Estimating selenium removal by sedimentation from the Great Salt Lake,Utah     

Wade Oliver  Christopher Fuller  David L. Naftz  William P. Johnson  Ximena Diaz 《Applied Geochemistry》2009

The mass of Se deposited annually to sediment in the Great Salt Lake (GSL) was estimated to determine the significance of sedimentation as a permanent Se removal mechanism. Lake sediment cores were used to qualitatively delineate sedimentation regions (very high to very low), estimate mass accumulation rates (MARs) and determine sediment Se concentrations. Sedimentation regions were defined by comparison of isopach contours of Holocene sediment thicknesses to linear sedimentation rates determined via analysis of ²¹⁰Pb, ²²⁶Ra, ⁷Be and ¹³⁷Cs activity in 20 short cores (<5 cm), yielding quantifiable results in 13 cores. MARs were developed via analysis of the same radioisotopes in eight long cores (>10 cm). These MARs in the upper 1–2 cm of each long core ranged from 0.019 to 0.105 g_sed/cm²/a. Surface sediment Se concentrations in the upper 1 or 2 cm of each long core ranged from 0.79 to 2.47 mg/kg. Representative MARs and Se concentrations were used to develop mean annual Se removal by sedimentation in the corresponding sedimentation region. The spatially integrated Se sedimentation rate was estimated to be 624 kg/a within a range of uncertainty between 285 and 960 kg/a. Comparison to annual Se loading and other potential removal processes suggests burial by sedimentation is not the primary removal process for Se from the GSL.  相似文献   

LIU TUNGSHENG'S PALAEOMAGNETIC LOESS RESEARCH IN SWITZERLAND          下载免费PDF全文

Friedrich Heller 《第四纪研究》2009,29(5):847-850

编者按　11月22日是刘东生先生的生日,在先生离开我们的一年多时间里,我们时刻在怀念他。这里我们刊登了刘先生的密友之一、瑞士的Heller教授的短文,怀念与刘先生一起研究黄土磁学的点点滴滴。本文是Heller教授为刘先生的纪念文集撰写的,但因故未及在文集中刊出。现在本刊补登,除了表示对先生的深切怀念,也表示对Heller教授的感谢和歉意。  相似文献   

Decoding the complex internal chemical structure of garnet porphyroblasts from the Zermatt area,Western Alps   总被引：1，自引：0，他引：1  

Kurt Bucher  Tobias Bjrn Weisenberger  Oliver Klemm  Sebastian Weber 《Journal of Metamorphic Geology》2019,37(9):1151-1169

Garnet is a prototypical mineral in metamorphic rocks because it commonly preserves chemical and textural features that can be used for untangling its metamorphic development. Large garnet porphyroblasts may show extremely complex internal structures as a result of a polycyclic growth history, deformation, and modification of growth structures by intra‐ and intercrystalline diffusion. The complex internal structure of garnet porphyroblasts from garnet–phengite schists (GPS) of the Zermatt area (Western Alps) has been successfully decoded. The centimetre‐sized garnet porphyroblasts are composed of granulite facies garnet fragments overgrown by a younger generation of grossular‐rich eclogite facies garnet. The early granulite facies garnet (G‐Grt) formed from low‐P, high‐T metamorphism during a pre‐Alpine orogenic event. The late garnet (E‐Grt) is typical of high‐pressure, low‐temperature (HPLT) metamorphism and can be related to Alpine subduction of the schists. Thus, the garnet of the GPS are polycyclic (polymetamorphic). G‐Grt formation occurred at ~670 MPa and 780°C, E‐Grt formed at ~1.7 GPa and 530°C. The G‐Grt is relatively rich in Prp and poor in Grs, while E‐Grt is rich in Grs and poor in Prp. The Alm content (mol.%) of G‐Grt is 68 of E‐Grt 55. After formation of E‐Grt between and around fragmented G‐Grt at 530°C, the GPS have been further subducted and reached a maximum temperature of 580°C before exhumation started. Garnet composition profiles indicate that the initially very sharp contacts between the granulite facies fragments of G‐Grt and fracture seals of HPLT garnet (E‐Grt) have been modified by cation diffusion. The profiles suggest that Ca did not exchange at the scale of 1 µm, whereas Fe and Mg did efficiently diffuse at the derived maximum temperature of 580°C for the GPS at the scale of 7–8 µm. The Grt–Grt diffusion profiles resulted from spending c. 10 Ma at 530–580°C along the P–T–t path. The measured Grt composition profiles are consistent with diffusivities of log D_MgFe = ?25.8 m²/s from modelled diffusion profiles. Mg loss by diffusion from G‐Grt is compensated by Fe gain by diffusion from E‐Grt to maintain charge balance. This leads to a distinctive Fe concentration profile typical of uphill diffusion.  相似文献   

Geomorphometric feature analysis using morphometric parameterization and artificial neural networks   总被引：3，自引：0，他引：3  

Amir Houshang Ehsani  Friedrich Quiel 《Geomorphology》2008,99(1-4):1-12

This paper presents a semi-automatic method using an unsupervised neural network to analyze geomorphometric features as landform elements. The Shuttle Radar Topography Mission (SRTM) provided detailed digital elevation models (DEMs) for all land masses between 60°N and 57°S. Exploiting these data for recognition and extraction of geomorphometric features is a challenging task. Results obtained with two methods, Wood's morphometric parameterization and the Self Organizing Map (SOM), are presented in this paper.Four morphometric parameters (slope, minimum curvature, maximum curvature and cross-sectional curvature) were derived by fitting a bivariate quadratic surface with a window size of 5 by 5 to the SRTM DEM. These parameters were then used as input to the two methods. Wood's morphometric parameterization provides point-based features (peak, pit and pass), line-based features (channel and ridge) and area-based features (planar). Since point-based features are defined as having a very small slope when their neighbors are considered, two tolerance values (slope tolerance and curvature tolerance) are introduced. Selection of suitable values for the tolerance parameters is crucial for obtaining useful results.The SOM as an unsupervised neural network algorithm is employed for the classification of the same morphometric parameters into ten classes characterized by morphometric position (crest, channel, ridge and plan area) subdivided by slope ranges. These terrain features are generic landform element and can be used to improve mapping and modeling of soils, vegetation, and land use, as well as ecological, hydrological and geomorphological features. These landform elements are the smallest homogeneous divisions of the land surface at the given resolution. The result showed that the SOM is an efficient scalable tool for analyzing geomorphometric features as meaningful landform elements, and uses the full potential of morphometric characteristics.  相似文献   

Assessment of metal concentrations found within a North Sea drill cuttings pile     

Breuer E  Shimmield G  Peppe O 《Marine pollution bulletin》2008,56(7):1310-1322

North Sea drill cuttings piles are a distinct anthropogenic legacy resulting from the exploration and production of North Sea oil reserves. The need to understand metal cycling within the piles becomes increasingly important with the imminent decommissioning of many North Sea platforms and the subsequent fate of associated cuttings piles. This paper presents results of the simultaneous analysis of geochemical carrier substances (Mn and Fe oxyhydroxides), along with dissolved (<0.2 microm) and total (>0.2 microm) metal (Ba, Co, Cr, Cu, Mo, Pb, V) concentrations from a North Sea cuttings pile and surrounding sediment. These data are examined in conjunction with in situ measured porewater oxygen and sulfide. Results show a rapid removal of oxygen within the top few millimeters of the cuttings pile along with elevated concentrations of total hydrocarbons and solid phase metal concentrations compared to the surrounding environment.  相似文献   

Galaxy and cluster biasing from Local Group dynamics     

M. Plionis  S. Basilakos  M. Rowan-Robinson  S. J. Maddox  S. J. Oliver  O. Keeble  W. Saunders 《Monthly notices of the Royal Astronomical Society》2000,313(1):8-12

Comparing the gravitational acceleration induced on the Local Group of galaxies by different tracers of the underlying density field we estimate, within the linear gravitational instability theory and the linear biasing ansatz, their relative bias factors. Using optical SSRS2 galaxies, IRAS (PSC z ) galaxies and Abell/ACO clusters, we find b _O,I≈1.21±0.06 and b _C,I≈4.3±0.8, in agreement with other recent studies. Finally, there is an excellent one-to-one correspondence of the PSC z and Abell/ACO cluster dipole profiles, once the latter is rescaled by b _C,I, out to at least ∼150  h ⁻¹ Mpc.  相似文献   

News from the Lower Ionosphere: A Review of Recent Developments   总被引：1，自引：1，他引：0  

M. Friedrich  M. Rapp 《Surveys in Geophysics》2009,30(6):525-559

Current knowledge concerning the lower ionosphere (D- and E-region) is reviewed with an emphasis on new aspects of empirical results. Starting with an overview of experimental techniques and corresponding data bases, both regarding charged as well as the most relevant neutral constituents of this altitude range, the ionospheric variability is discussed both concerning regular (e.g. diurnal and seasonal) as well as irregular variations (e.g. driven by the variability of nitric oxide). We then turn to ‘new players’ in the lower ionosphere, i.e. charged aerosol particles such as mesospheric ice particles in noctilucent clouds or polar mesospheric summer echoes and meteor smoke particles originating from ablated meteoric matter. These species have received considerable attention in recent years, in part because it is speculated that observations of their properties might be useful for the detection of climate change signals. The available experimental data base regarding these species is reviewed and we show that there is now compelling evidence for the ubiquitous presence of these very heavy charge carriers throughout the lower ionosphere. While many fundamental details regarding these charged species are not yet completely understood, this emphasizes that charged aerosol particles may not be neglected in a comprehensive treatment of the lower ionospheric charge balance and related phenomena. Finally, we close with suggestions for future research.  相似文献   

The impact of upland land management on flooding: results from an improved pasture hillslope   总被引：1，自引：0，他引：1  

Miles R. Marshall  Oliver J. Francis  Zoe L. Frogbrook  Bethanna M. Jackson  Neil McIntyre  Brian Reynolds  Imogen Solloway  Howard S. Wheater  Joanne Chell 《水文研究》2009,23(3):464-475

In response to growing concern about impacts of upland agricultural land management on flood risk, an intensely instrumented experimental catchment has been established at Pontbren, a sheep‐farmed headwater catchment of the River Severn, UK. Primary aims are to develop understanding of the processes governing flood generation and the associated impacts of land management practices, and to bridge the gap between process understanding and ability to predict effects on downstream flooding. To achieve this, the experiment is designed to operate at plot (～100 m²), hillslope (～0·1 km²) and small catchment scale (～10 km²). Hillslope‐scale data, from an under‐drained, agriculturally ‘improved’ pasture, show that drain flow is a dominant runoff process. However, depending on antecedent moisture conditions, overland flow may exceed drain flow rates and can be an important contributor to peak flow runoff at the hillslope‐scale. Flow, soil tension data and tracer tests confirm the importance of macropores and presence of perched water tables under ‘normal’ wet conditions. Comparisons of pasture runoff with that from within a 10 year‐old tree shelterbelt show significantly reduced overland flow due to the presence of trees and/or absence of sheep. Comparisons of soil hydraulic properties show significant increases in hydraulic conductivity and saturated moisture content of soil under trees compared to adjacent improved pasture. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献